The internal structures of houses and other buildings are commonly protected from environmental elements by exterior siding materials. These siding materials are typically planks or panels composed of wood, concrete, brick, aluminum, stucco, wood composites, or fiber-cement composites. A common fiber-cement composite is fiber-cement siding, which is generally composed of cement, silica sand, unbleached wood pulp, and various additives. Fiber-cement siding offers several advantages over other types of siding materials, such as wood siding: it is weatherproof, relatively inexpensive to manufacture, fire-resistant, and invulnerable to rotting or insect damage.
Commercial fiber-reinforced cement siding planks or panels are made using the Hatsheck process. The Hatsheck process was initially developed for the production of asbestos composites, but it is now used for the manufacture of non-asbestos, cellulose fiber reinforced cement composites. In this process, unbleached cellulose fibers are re-pulped in warm water at an alkaline pH of 11 to 12.5; the re-pulped fibers are refined and then mixed with cement, silica sand, and other additives to form a mixture. The fiber-cement mixture, is deposited on a felt band substrate, vacuum dewatered, and cured to form a fiber reinforced cement matrix in sheet form.
The curing of the cement matrix is hindered by the presence of sugars or other organic materials. These materials retard the hydration reaction of cement and thereby retard the setting or hardening of a mortar or concrete. Cement is purposely retarded in ready-mix concrete during long hours of transportation, for mitigation of stress due to temperature (heat) when used in a large-sized concrete structures, and for decorated washing finishes. When these organic materials are measured, the manufacturers of fiber-cement siding have observed an inverse relationship between the amount of these materials in an unbleached pulp and the strength properties of the final product. The amount of these materials is commonly measured using the chemical oxygen demand (COD) test. When considering the detrimental effect of these materials on strength properties, it is apparent that there are a needs in the art for very low COD unbleached pulp. The present invention fulfills these needs and provides further related advantages.